Solder Volume Effect on the Microstructure of Solder Joints Using Au/Pd(P)/Ni(P) Surface Finish

The liquid-solid reaction between Sn3Ag0.5Cu and Au/Pd(P)/Ni(P) tri-layer with three different joint diameters (d(joint)), 200 mu m, 150 mu m, and 60 mu m, were investigated in this study. The reaction product(s) strongly depended on d(joint). In the case of d(joint) = 200 mu m, the predominant product after reaction at 245 degrees C for 80 s was a continuous (Cu,Ni)(6)Sn-5. When d(joint) slightly reduced to 150 mu m, a mixture of (Cu,Ni)(6)Sn-5 and (Ni,Cu)(3)Sn-4 grew at the interface. When d(joint) further reduced to 60 mu m, the (Cu,Ni)(6)Sn-5 was completely replaced by (Ni,Cu)(3)Sn-4. Moreover, a significant amount of isolated (Pd,Ni)Sn-4 domains scattered inside the solder matrix near the interface. The transition of the microstructure was attributed to the decrease of Cu concentration (C-Cu) and increase of Pd concentration (C-Pd) as d(joint) reduced. This finding suggests that the solder volume is an important factor in determining the microstructure of solder joints. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of MRS-Taiwan